title: Rapid diversification of marine picophytoplankton with dissimilar light-harvesting structures inferred from sequences of Prochlorococcus and Synechococcus (Cyanobacteria).
abstract: Cultured isolates of the unicellular planktonic cyanobacteria Prochlorococcus and marine Synechococcus belong to a single marine picophytoplankton clade. Within this clade, two deeply branching lineages of Prochlorococcus, two lineages of marine A Synechococcus and one lineage of marine B Synechococcus exhibit closely spaced divergence points with low bootstrap support. This pattern is consistent with a near-simultaneous diversification of marine lineages with divinyl chlorophyll b and phycobilisomes as photosynthetic antennae. Inferences from 16S ribosomal RNA sequences including data for 18 marine picophytoplankton clade members were congruent with results of psbB and petB and D sequence analyses focusing on five strains of Prochlorococcus and one strain of marine A Synechococcus. Third codon position and intergenic region nucleotide frequencies vary widely among members of the marine picophytoplankton group, suggesting that substitution biases differ among the lineages. Nonetheless, standard phylogenetic methods and newer algorithms insensitive to such biases did not recover different branching patterns within the group, and failed to cluster Prochlorococcus with chloroplasts or other chlorophyll b-containing prokaryotes. Prochlorococcus isolated from surface waters of stratified, oligotrophic ocean provinces predominate in a lineage exhibiting low G + C nucleotide frequencies at highly variable positions.
authors.affiliation: Ralph M. Parsons Laboratory, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.
authors.forename: E
authors.initials: E
authors.lastname: Urbach
authors.forename: D J
authors.initials: DJ
authors.lastname: Scanlan
authors.forename: D L
authors.initials: DL
authors.lastname: Distel
authors.forename: J B
authors.initials: JB
authors.lastname: Waterbury
authors.forename: S W
authors.initials: SW
authors.lastname: Chisholm
mesh_terms: D000818:Animals; D001426:Bacterial Proteins / Q000235:genetics; D001483:Base Sequence; D000458:Cyanobacteria / Q000145:classification / Q000235:genetics* / Q000502:physiology; D003573:Cytochrome b Group / Q000235:genetics; D045346:Cytochrome b6f Complex; D018014:Gene Transfer Techniques; D008969:Molecular Sequence Data; D045524:Phycobilisomes; D010802:Phylogeny; D010839:Phytoplankton / Q000382:microbiology*; D010940:Plant Proteins / Q000235:genetics; D016133:Polymerase Chain Reaction; D012336:RNA, Ribosomal, 16S; D017422:Sequence Analysis, DNA; D012689:Sequence Homology, Nucleic Acid
chemical_list: D001426:Bacterial Proteins; D003573:Cytochrome b Group; C104657:PetB protein, plant; D045524:Phycobilisomes; D010940:Plant Proteins; D012336:RNA, Ribosomal, 16S; C084072:petD protein, cytochrome b(6)f complex; D045346:Cytochrome b6f Complex